On the afternoon of June 13, 1805, the expedition arrived at the first of the five falls. Lewis described the falls and made careful notes of the heights of each. The first and highest stood at almost 90 feet. From start to finish, the falls brought the level of the Missouri down almost 400 feet. Lewis' journal called the falls a

"truly magnificent and sublimely grand object which has from the commencement of time been concealed from the view of civilized man."

Lewis didn't have much more time to appreciate the view before being chased into the river by yet another grizzly bear. He crouched in the water and pointed his espontoon (a sort of multi-purpose spear carried by most of the expedition members for defense, climbing and other uses). The bear declined to enter the deeper water and ran off at top speed.

While returning to camp, he was assaulted again by what he described as a large cat "of the tiger kind." He fired on it, and it disappeared into its burrow. Although he first mistook it for a wolf, some historians believe it was a bobcat, and others a mountain lion. Whatever it was, Lewis felt somewhat put upon:

"It now seemed to me that all the beasts of the neighbourhood had made a league to distroy me, or that some fortune was disposed to amuse herself at my expence, for I had not proceded more than three hundred yards from the burrow of this tyger cat, before three bull buffaloe - seperated from the herd and ran full force towards me - they made a halt, took a good view of me and retreated with precipitation."

The route around the series of falls presented one of the greatest obstacles faced by the expedition. Lewis and Clark had believed the portage around the falls would take a week at most. It took them a month to emerge from this ordeal. Lewis felt the need for haste and caution as the Corps was spread thin:

"Not haveing seen the Snake Indians or knowing in fact whither to calculate on their friendship or hostillity, we conceived our party sufficiently small, and therefore have concluded not to dispatch a canoe with a part of our men to St. Louis as we have entended early in the Spring."

The captains, in their first report to Jefferson sent from Fort Mandan, wrote of their intention to send another from Great Falls. Rumors that they had perished began to circulate in the east when this second report failed to arrive.

The portage meant passing through 18 miles of mosquitoes, gnats, rattlesnakes, and grizzlies. Men in moccasins, harnessed to primitive wagons with wheels cut from tree-trunks, hauled six canoes and all their baggage over rutted buffalo trail covered in cactus. Eight trips each way were required to finish the job.

Lewis described the 18 1/4-mile trip and the labor involved in hauling their makeshift wagons across rough soil studded with cactus. The men wore double-soled moccasins, but there were barely enough of them to move the trucks. Some of the men had been sent off to hunt.

Rough weather assaulted them on the way. Hailstones that were "7 inches in circumference and waied 3 ounces, fortunately for us it was not so large (on the whole route) if it had we should most certainly have fallen victims to its rage as the men were mostly naked, and but a few with hats or any covering on their heads." Wind gales proved useful as "the men informed me that they hoisted a sail in the canoe and it had driven her along on the truck wheels."

Finally, at the White Bear Islands, the Corps tried to assemble a collapsible iron-frame boat of Lewis' design.

Parts for the 36-foot, ninety pound iron boat frame were brought with great effort from the Federal Armory at Harper's Ferry, Virginia (later West Virginia). Plans to attach over 30 animal skins and hides to the frame were foiled by a lack of materials and the right needles to stitch the hides together. The assembled boat sank repeatedly, despite vain attempts to plug leaks with beeswax, lard and finally charcoal. Lewis was despondent, but the delay did allow time to dry fish and meat for the long trip to the mountain ranges that finally came into view. They carved two dugout canoes instead.

A flash flood nearly washed Sacagawea, her son, and Clark away on June 29, while the Corps moved through a ravine. Several pieces of equipment were lost in the torrent. On July 4, a celebration consumed the last of the company's alcohol. Mosquitoes and illness took a toll on many, including Sacagawea, but the portage that had begun June 21 was completed on July 15, 1805. The Corps of Discovery moved on to Three Forks and the Missouri Headwaters.